Structured as an hour-long second feature, it is the final entry in the eight-film low-budget series which centers on the bond between the German Shepherd dog Rusty and the boy Danny Mitchell, portrayed by Ted Donaldson.

[2] Rusty pulls the mailbox string, clamps his jaws around the letter inside and brings it into the kitchen where city legal official Hugh Mitchell is instructing his teenage son Danny on baking four rainbow trout.

Meanwhile, Rusty takes his other present, a small ball and exits into the backyard where he confronts a vagrant who then throws a wrench at him and runs to a gas station, just as a middle-aged woman drops her purse before getting into a car with her husband.

Attorney Mitchell telephones to place a newspaper ad regarding Rusty's disappearance, while Danny and his four friends from the neighborhood return after an unsuccessful search.

A young boy named Jeff Neeley, pulling a stuffed toy dog on a string, rescues Rusty, taking him to be the personification of his imaginary dog friend "Gladly" and leads him to the campsite where his older brother Bill and unemployed sharecropper father Virgil, sitting alongside a small dilapidated truck, are cooking food from their meager supply.

Moments later, Danny and the boys spot Bill and Jeff who are sitting at the curb, next to the truck, examining Rusty's paw.

Later, as Bill is helping Virgil repair the cabin that will be their new living place, Miss Simmons arrives with a freshly baked pie.

Jack Wiggins, the gas station owner/attendant, explains to a gathering of locals that "…when I got back, I found this character looting the cash register".

The vagrant is brought into the Mitchell house where a confrontation with Rusty makes him blurt out that he didn't steal the dog, but only sold him.

Later, as the Mitchells discuss Danny's behavior, he returns home and tells them that "Bill is a great guy" and "how wonderful it is to have a permanent address".

As the Mitchells came home from the hospital with the news that Virgil Neeley is out of danger, Danny offers to give up Rusty so that Jeff can have his "Gladly" and live with the Mitchells while he is at military school, his parents tell him that there is no need for any of that, since Jeff will be happy with his father and Miss Simmons, to whom "he's transferred his heart… lock, stock and barrel".